A Back-to-Back Ligand with Dipyrazolylpyridine and Dipicolylamine Metal-Binding Domains

Reaction of 4‐bromomethyl‐2,6‐bis(pyrazol‐1‐yl)pyridine with dipicolylamine yields 4‐bis(pyrid‐2‐ylmethyl)aminomethyl‐2,6‐bis(pyrazol‐1‐yl)pyridine (L). Treatment of L with [MCl2(NCPh)2] (M = Pd, Pt) in the presence of AgPF6 affords [MCl(L)]PF6, whose palladium or platinum centre is bound exclusively by the dipicolylamino moiety of L, as established by NMR spectroscopy. The pendant dipyrazolylpyridine residue in these compounds is complexed by iron(II) to form [Fe{MCl(μ‐L)}2][PF6]4 (M = Pd, 1; M = Pt, 2·nH2O). The nitromethane solvate crystal of 1 contains low‐spin iron centres at 150 K. However, dried 1 and 2·nH2O are predominantly high‐spin at room temperature, undergoing very gradual thermal spin transitions upon cooling to ≤ 50 % completeness. The platinum compound also undergoes a thermal spin transition in CD3NO2 solution, with T1/2 = 253 K. The new ligand 4‐bis(pyrid‐2‐ylmethyl)aminomethyl‐2,6‐bis(pyrazol‐1‐yl)pyridine(L) is metallated sequentially at its dipicolylamino and then its dipyrazolylpyridylsites. The FeM2 (M = Pd and Pt) complexes undergo gradual thermal spin transitions in the solid state and (when M = Pt) in solution.